There are numerous prior art patents and commercial products relating to security documents that have different types of printing on them. One type of printing can be resolved by conventional photocopy machines (such as xerographic copiers), while the other printing cannot be resolved by conventional photocopy machines and, therefore "disappears" if the document is copied. By providing the disappearing printed matter in a particular configuration that provides a warning indicia (such as the words "VOID"), a clear indication will be provided on the copied document that it is not an appropriate document and, therefore, hopefully will not be able to be used for illegal purposes. Security documents to which these techniques are applied typically are bank checks, titles to real and personal property, and the like.
While prior art security documents have been successful in preventing accurate nefarious production under many circumstances, some prior art security documents having this capability look somewhat unusual to many users. On some such documents, the warning indicia are not effectively hidden, which can make a legitimate document subject to question, while on other such documents the warning indicia are provided on only a small part of the document, or in an unusual and un-esthetically dense pattern.
According to the present invention, a security document is provided that has the same utility as prior art security documents in providing a warning indicia if copied by conventional photocopy machines, but the configuration of the printed matter is such that it is more pleasing esthetically than many conventional security documents, does not have inordinately dense printed areas, and in general has an interspersing of blank areas with printed areas in a distinct continuous intermeshed pattern such that the warning printed matter is indistinguishable from the printed background by the human eye.
According to one aspect of the present invention, a security document that, if copied by a photocopy machine, provides an indication that it has been copied comprises the following elements. A substrate having a surface receiving printing. A first plurality of printed elements visible to the human eye as lines extending in a first direction parallel to each other, and dimensioned so that they can be resolved by a photocopy machine. A second plurality of printed elements visible to the human eye as lines extending in the first direction and parallel to each other, and appearing to the human eye as continuations of the first plurality of printed elements, and dimensioned so that they cannot be resolved by a photocopy machine, the second plurality of elements disposed in a configuration forming invalidating indicia if the document is copied by a photocopy machine. The printed elements have a density of less than 20%, and the printed elements are disposed in a pattern that is continuous over the majority of the surface, interspersed with blank areas of the surface, so that the elements collectively establish a pattern that is seen by the human eye as a continuous pattern in which the invalidating indicia are not visible unless the document is copied by a photocopy machine. Typically, the first printed elements are lines and the second printed elements are dots.
Normally the substrate has a quadrate configuration including two end edges and two side edges, and the first lines are preferably parallel to two of the edges of the substrate. To provide an appropriate density some of the dots may be disposed in additional in-line configurations parallel to the geometric continuations of some of the first lines, and disposed equidistant between two of the geometric continuations.
The techniques according to the present invention are particularly applicable for utilization when the warning printed matter is disposed in the form of at least one outline letter configuration, and normally in a plurality of outline letter configurations such as the letters making up the word "VOID". An outline letter configuration per se is described in U.S. Pat. No. 4,420,175, the disclosure of which is hereby incorporated by reference herein. According to the present invention, when an outline letter configuration is provided for the first warning printed matter, a second printed background pattern is disposed on the surface within the outline letter configuration, and comprises a plurality of second parallel lines extending in a third direction, the second lines of a size such that they will be resolved by a photocopying machine. This third direction makes an angle of between 20-70.degree. (e.g., 45.degree.) with respect to an edge of the substrate. For certain letter configurations (such as the "O" and "D" in the word "VOID"), second warning printed matter dots in a repeat form of the same outline letter are disposed inside of the second parallel lines forming a continuation of some of the second parallel lines, and a third printed background pattern may be provided on the surface disposed within the second dots outline configuration and providing lines which are a geometric continuation of the first lines.
The density of the various printed portions will be varied depending upon the color, particular pattern (e.g., herringbone) of the printed matter, and the like, but typically are within the range of about 7-15%, e.g., 7-11%, and more particularly about 9-11% for the background printed matter. The dots, which may be circular, have an average maximum cross dimension of no more than 0.0076 cms (three thousandths of an inch) so that they do not reproduce accurately. The lines -- since they have a significant length -- may have a width that is about 0.0076 cms, and will reproduce.
It is a primary object of the invention to provide a simple yet effective security document that in its normal configuration presents a distinct continuous intermeshed pattern in which warning printed matter is indistinguishable from the background printed matter by the human eye, yet when copied by a photocopy machine provides clear warning indicia. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.